The present invention relates to diagnostics of process devices (for use with industrial processes). More specifically, the invention relates to diagnostics of processes using a process variable sensor signal.
Process control devices are used in industrial process control systems to control a process. A control device is a field device which is used to control the process and includes pumps, valves, actuators, solenoids, motors, mixers, agitators, breaker, crusher, roller, mill, ball mill, kneader, blender, filter, cyclone, centrifuge, tower, dryer, conveyor, separator, elevator, hoist, heater, cooler or others. A valve controller includes a valve actuator coupled to a valve used to control flow of process fluid. A pump controller includes a motor controller or actuator coupled to a pump. Diagnostics of process control devices can be used to identify a failed control device or predict an impending failure.
Sensing vibrations is one method used to diagnose process control devices. A vibration sensor such as an accelerometer placed directly on a control device can be used to sense vibration noise signals generated by the device. Vibrations are isolated and evaluated by identifying those which exceed an amplitude threshold or which have an abnormal frequency which are indicative of an actual or impending failure. For example, sensors are placed on pump or motor housings, discharge valves, or flanges associated with the control device. Another known diagnostic method is a manual inspection in which an operator listens for abnormal sounds from the control device.
These known methods rely on sensing vibrations at the process control device. The automated diagnostic techniques require additional sensors and circuitry to be included in the control device. There is thus a need for improved diagnostic technology which does not rely on additional components in the control device or the inaccurate and time consuming manual inspection of the prior art to isolate and evaluate vibration noise signals.
Diagnostics for diagnosing process devices isolates and evaluates vibration noise signals in the process fluid using a process variable sensor signal. The signal preprocessor isolates signal components in the sensor signal related to operation of the process and provides an isolated signal output. A signal evaluator provides a condition output related to a condition of the process control device as a function of the isolated signal. The diagnostic device is in a process control system, and vibrations from the process are transferred through process fluid to a process variable sensor used by the diagnostic device. A sensor input receives the process variable sensor signal from the process variable sensor. A portion of the sensor signal is related to the vibrations in the process which are carried in the process fluid.